Mudslides can not at present be forecast with any degree of accuracy although there are predictable precursor ingredients that may well contribute to a disaster.

Twenty four people have been trapped by a slide just north of San Bernardino in California. A torrent of mud, boulders, logs and tree branches engulfed a youth camp based at Saint Sophia Camp in Waterman Canyon which sent the campers fleeing.

The torrent washed away bridges and the continued heavy rainfall has hampered rescue efforts to locate survivors. Ten people are still reported missing.

So what are some of the factors that caused this? The heavy rain is an obvious candidate. A winter storm dropped around seven centimetres of rain on the San Bernardino mountains, a heavy fall of rain, but by no means exceptional for a mountainous area.

There is however another important weather factor that is less obvious but is equally to blame for the incident, a time-bomb that was set just a few months ago; dry weather.

After months of dry weather in the summer, the largest wildfires in California history swept across the state singeing nearly a million acres of land in the region. Trees and other vegetation were stripped off the mountain slopes and consumed in the blaze.

Without the stabilising influence of the roots the slopes were left vulnerable and unstable. The rainwater would also have been able to pick up more speed down the slopes without the vegetation to slow its progress.

There was a predictable inevitability about this disaster, yet nobody could possibly have forecast it.

Weather News from the last five days:
25/12/2003
24/12/2003
23/12/2003
22/12/2003
21/12/2003

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